Early versions of Teradata Express included some small sample databases, but those were removed from later releases.
But new Teradata users usually ask for existing tables to start playing around. To make it easy I published several data sets on GitHub
For starters switching from SQL Server there's the well-known AdventureWorkDW, Microsoft's Data Warehouse sample database, ported to Teradata.
But I usually prefer real data over synthetic, thus there's a financial dataset based on real world transactions in the years 1993 to 1999 from a Czech bank, afaik the only publicly available banking data on the web. Eight tables (accounts, transactions, etc.) with up to 1,000,000 rows:
And there's a payroll dataset based on two Public Domain datasets published by the city of Baton Rouge, Louisiana. Six tables (employees, jobs, departments, etc.) with up to 54,000 rows: